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madkaw

Triple Mikuni thread

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Well some of you that I am now proceeding with my Mikuni install.When I purchased these carbs I got lucky and recieved a very complete kit. These look new right out of the box-infact the carbs came in a Mikuni box:) I even recieved an original 1985 catalog and service manual.

I decided to post up parts of these Mikuni publications on here for all to view. Between the two publications I have part numbers and illustrations of the carbs and their parts. Let me know if there is anything in particular that you might want to see. I know folks buy these carbs with the intent to rebuild, but not much to go on. I hope this thread and pics will help.

I'll start out with the some stuff from the catalog

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This is AWESOME! Would it be possible to make a PDF of the booklet and post it? Especially the tuning section.

May be asking too much, but thought I'd ask :)

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Not sure I know how to do a PDF file. I just barely get by with the computer stuff!!

I do plan on taking pics of the manual and posting them also. Maybe with some guidance I can make a zip file with all the pages in one folder.

Are the pages readable as I have presented them??

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Walter,

love to do that. Don't ever mind showing off the Z!

As far as the Mikuni info, another member has volunteered to make a PDF file and host it. I am in the process of scanning the stuff and sending it to him now, so hopefully this will be available soon.

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As I press on with my install of the Mikuni's I will try and document the process with pictures and also note things of interest or things to be aware of.

First of I will make note of the Mikuni shorty manifold and the issues with it. Mitchell will testify that mounting it is a pain in the a$$. Because the runners turn sharply there is little room for the studs and nuts. If the studs are too long you will run into issues with them hitting the manifold and the manifold not seating properly. So the studs MUST be correct. I was supplied with studs with my kit, but they were so short I only got a few threads in some of the nuts. Since my SU's were mounted on studs, I just tailor fitting them by cuttting of threads until I got the proper length-again, a lot of work.

Also, the Mikuni manifold comes in contact with the thermostat housing. It is subtle and could be over looked until you started it up and noticed the huge vacuum leak. The flange on the housing where the aft bolt runs thru is too thick and causes the bolt head to hit the manifold. I just ground down the flange thickness so the bolt would clear. I also had a small clearance issue with the "bowl" part of the housing, or widest part of the housing-it is also close clearance on the intake.

The Mikuni manifold was the correct thickness to match the MSA header flange-so the washers work welll to secure everything.

The Mikuni manifold is tapped on every runner for -whatever. One hole is larger, #6, so it is good for brake vacuum size hose. All the rest are 1/8"NPT. I decided to gang all the ports together into a vacuum log. Note: I had to chase all the holes with a tap to get the barb fitting to screw all the way in.

Another note: the diameter of the ports on the intake runners are considerably smaller then the ports on the head . This is purposely done as anti-reversion. My manifold was built specifically for the Z car and I believe Mikuni knows what there doing. It does look way different then the SU manifold, but don't be tempted to port match the manifold to the gasket-unless you making a screamer. I thought I had a pic, but I can't find it right now.

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Edited by madkaw

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Looking for a cheap way to fuel these triples would have been to use the original mechanical pump and regulator. The kit I got actually had some kind of reducer bushing that went inline with the original fuel line to reduce pressure I believe. I will post up the instructions to help better understand.

I went with the RX-7 pump, or a replacement pump for the RX-7. Rock-auto had them for a little as 40$ with everything you need-bracket, connecting hoses and clamps, and also an inline filter. I have read many good reports on them as being quiet and they also operate at the optimum pressure-2.5psi-4psi.

I attached mine to the floor in the hatch area. My car is very different then most since I run a centered tank and dual exhaust. It was tight and mounted the pump with some rubber to hide the noise. The pump gives off a slight padder sound that you can't hear when the car is running. I believe the pump was a Tilex.

The regulator is a Holley 1204. The fuel pressure guage is just a Summit guage, but it did come with a 90 degree fitting which was cool. Prepare to get adapter fittings for everything else on the regulator. The regulator comes 3/8NPT threads-which is way big for a 5/16" fuel line. I actually cut-off the original feed line and reused it by utilizing compression fittings. I flared the ends that hooked up to my filter so the hose had a good grip and didn't leak. I ran a clear filter to see how clean things are. I decided to NOT run return line. The kit I recieved had bango bolt fitting to run the fuel either way. So far no leaks!

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As far as linkage to operate the triples, the cable method would probably be best. It takes up less room and has less moving parts and people seem to be happy with the results--so that's why I did the rod linkage:)

Actually the kit provided some pieces to utilize the stock Z linkage, but I couldn't figure it out or I think I am missing some parts. I just had to come up with something to bridge between the firewall and the Mikuni linkage. I scrounged around(never throw away anything;)) and found something that I could modify that had a ball end on it.

The stock linkage for the carbs seems pretty stout. I have read of the Webers linkage being weak, but I don't see that with the Mikuni. Time will tell if my set-up will be smooth enough and strong enough. I haven't driven the car yet with the Mikuni's. The challenge for me is the enrichment linkage. I want to run the enrichment(chokes) for ease of starting and to keep from having to drown the carbs with fuel from the accelerator pumps to keep it running on a cold start. The problem is that I need to run a cable choke set-up and I'm running out of room with the linkage I have now. This is where the cable set-up would be beneficial in that I would gain room for the enrichment cable.

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Well I wish I would be reporting that the Mikunis are up and running- but there not:(

I will say that I have been talking to Todd at Wolfcreek and I am impressed. He might come off as gruff at first, but just think about all the dumb calls he gets. So if you plan on calling him for help or advice- be prepared to answer SPECIFIC questions and prepare to LISTEN.

Right now I have a decent idle and the car will rev-up well, but it actually stalls during a slow transition from idle. I have to adjust out the primaries 3 turns to get the car to idle. I have 57.5 primaries in there now.

180 main air

140 main jet

45 acceler nozzles

Todd recommended that I make sure the accelerator pumps are working. Sometimes it takes a while for them to prime. Also, check your floats by hanging them on their seats and measuring.

I can't way to drive and test out my CAI!

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This is AWESOME! Would it be possible to make a PDF of the booklet and post it? Especially the tuning section.

May be asking too much, but thought I'd ask :)

Just thought that I would mention that I found the MANUAL on this site and hybrid in PDF format. Just google and you will find it. I will post up the link when I can.

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What is your wideband telling you? I had a fairly bad transition stumble when I first installed my Mikuni's. I solved my issue by adding more fuel to both the idle and main circuit. I also had to purge the air out of the accelerator pump system as Todd mentioned. With a few minor jet tweaks I now have zero hesitation at any RPM or throttle position. It's been my experience that these cars tend to idle and accelerate/transition best at 11-12ish AFR with Mikuni's. Keep at it, once you get them tuned you will love them.

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steve,

I don't see how to richen up the idle without installing a bigger primary jets.

I'd like to know what jets you are running?

Did you work the accelerator pumps while on the car or off?

At this point I am thinking of pulling off the carbs and holding the butterflies open to see the pumps working.

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I have the following setup on my L30...

44mm carbs

34mm venturis

150 fuel jets

210 air

57.5 pilots (1.5 turns out)

1.8 needle/seat

45 pump jets

I ran the same setup on a bone stock L24 with a set of 145 fuel jets.

You can work the air out of the accelerator system by opening and closing the throttle while the fuel system is pressurized. You can do this when the engine is on or off. I did it by driving around stabbing the throttle periodically. It's a little tricky to see if the accelerator pumps are working but you might try taking off the air horns and using a mirror to look down the bore.

If you are lean at idle at 3 turns out then you might need bigger pilots but Todd is the guy to ask. Does your idle change the same for all 6 cylinders as you close your adjustment screws? On my L24 I found that some cylinders reacted differently than others. Eventually I found that I could get the smoothest running engine by adjusting each cylinder individually so that screwing the pilot adjuster in 1 turn had the same effect on the engine. In other words, I'd turn the adjustment screw in 1 turn and record the idle change for each cylinder one at a time. I would then adjust the individual adjustment screws so that one turn in resulted in the same effect on the engine. This resulted in some cylinders being set at 1.25 turns out while some were set at 1.75 out. I don't think this is your issue but you can use this technique to determine if all of the idle circuits are working the same. If you have a vacuum leak or some other sort of issue with one carb you may be able to spot the problem child this way.

Just my $0.02.

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I have the following setup on my L30...

44mm carbs

34mm venturis

150 fuel jets

210 air

57.5 pilots (1.5 turns out)

1.8 needle/seat

45 pump jets

I ran the same setup on a bone stock L24 with a set of 145 fuel jets.

You can work the air out of the accelerator system by opening and closing the throttle while the fuel system is pressurized. You can do this when the engine is on or off. I did it by driving around stabbing the throttle periodically. It's a little tricky to see if the accelerator pumps are working but you might try taking off the air horns and using a mirror to look down the bore.

If you are lean at idle at 3 turns out then you might need bigger pilots but Todd is the guy to ask. Does your idle change the same for all 6 cylinders as you close your adjustment screws? On my L24 I found that some cylinders reacted differently than others. Eventually I found that I could get the smoothest running engine by adjusting each cylinder individually so that screwing the pilot adjuster in 1 turn had the same effect on the engine. In other words, I'd turn the adjustment screw in 1 turn and record the idle change for each cylinder one at a time. I would then adjust the individual adjustment screws so that one turn in resulted in the same effect on the engine. This resulted in some cylinders being set at 1.25 turns out while some were set at 1.75 out. I don't think this is your issue but you can use this technique to determine if all of the idle circuits are working the same. If you have a vacuum leak or some other sort of issue with one carb you may be able to spot the problem child this way.

Just my $0.02.

Well I have established for sure that not all of my accelerator pump nozzles are shooting fuel. I decided to remove everything to replace my intake gasket-since I reused my old one. The old gasket didn't show leaks under idle, but I needed to eliminate any possibilities or guessing.

Since I removed the carbs from the intake i could have a clear view of what's going on. #1 cylinder had NO fuel coming out of the nozzle, while #2(same carb) shot out 3 feet in the air-and almost in my eye:stupid:

The second carb was a little better, but small amounts of tip-in of the throttle showed that the nozzle wasn't 100%. You should see a bit of projectile fuel with the smallest of throttle movement. Any lack of fuel would show up as a dead spot in transition while driving.

I pulled out the nozzles to check cleaniness and make sure all ports were clear. Todd also told me to make sure the packing washer is there under the nozzle when you remove it. Another note about nozzles are that they are keyed and will only fit in the carb body one way. They are keyed to make sure the squirter hole faces down the port. When you drop the nozzle back in the carb body-it should fit flush with the top. The picture is the nozzle IMPROPERLY installed-notice how it sticks out!

I did drop the cover off the bottom of the carb that covers the diaphram of the accelerator pump, and it looked great. So for some reason I am not getting fuel into the nozzle cavity so it will squirt out.

Steve, I tried pumping the "air" out by filling the body with fuel and operating the throttle-MANY TIMES! I could only get fuel to come out one of the nozzles, I must have a blockage somewhere or the check ball is stuck, not sure how to clear that up, but I haven't done any compressed air yet.

After talking to Todd, I readjusted the floats. See the picture for proper adjustment. Todd said he likes to see 13mm between the lid(with gasket installed) and the top of the float. Measure at a point parallel with the brass tube in the background-roughly in the middle. The manual calls for 12mm-12.5mm.

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Sounds like you found your problem. I'm looking forward to hearing what's stopping flow to some of the accelerator circuits. Keep us posted.

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Well I took accelerator pumps and nozzles out and blew some compressed air thru the passages and looked things over. Really couldn't see anything that would cause any problems, but there was something somewhere, because the nozzles are all shooting equally:beer:

Then I pulled out the pilot screws and bad news(see pic). This is why you don't use any force whatsoever when bottoming out the screws. Someone really cranked on these and actually left a step in the mild brass screws. Todd has 6 new ones coming! I have some larger pilot air jets coming also incase.

Soooo-while I am waiting around for parts I decided to put some heat barrier on my intake. Not sure about some of the other heat shields out there, but the one I made doesn't go all the way under the intake, just the carbs. I got some Thermo-tech adhesive backed stuff and wrapped the bottom side of the intake.

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Good news, easy fix! I like your heat barrier idea. Let us know how it works out. I'm always looking for anything that will keep the carbs cooler here in Texas.

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I am not sure keeping heat from your intake is a good idea. The extra heat into the manifold is needed to keep the fuel a vapor. There are many paper written about this. In a nutshell, keeping the intake warm helps keep the fuel in a vapor state. Too cool, it can puddle and not stay vaporized. Keeping the carbs cool is good, but a properly warm intake is good idea in many cases.

for the most part, I think wrapping the intake will only prolong how long it takes to get to operating temperature. Just a thought.

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I am not sure keeping heat from your intake is a good idea. The extra heat into the manifold is needed to keep the fuel a vapor. There are many paper written about this. In a nutshell, keeping the intake warm helps keep the fuel in a vapor state. Too cool, it can puddle and not stay vaporized. Keeping the carbs cool is good, but a properly warm intake is good idea in many cases.

for the most part, I think wrapping the intake will only prolong how long it takes to get to operating temperature. Just a thought.

I agree, at least for a carb'd car. Keeping the intake warm is a necessity, unless you want to run really rich. This is why air-cooled engines require overly rich mixtures, as they have a huge "Tau layer" in their intake, "Tau layer" referring to the liquified fuel film in the intake. Rich mixtures must be used to cover up any lean holes during operation. It may work okay for racing applications, but you may be better off going without.

Nice job though, should be a good experiment nonetheless! You'll never know until you try. Those triples will be roaring soon enough!

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Good point guys. Honestly, I didn't think my wrap job would do anymore then keep the extreme heat from the header away from the bottom of the intake and keep the fuel charge a bit cooler. The wrap is only on the bottom half of each runner, and I believe there will still be plenty of heat in the intake.

I also thought I have searched and found guys that have run a heat shield all the way up against the head, so this would be different?

I would also consider the length of my intake runners-2"- maybe. Now how long are the VW runners. Just think how far the Mikuni pumps spray fuel-direct injection!! Not sure if any pooling is going to happen on this intake.

I was actually worried more about heat transfer from the intake to the carbs.

Besides-you know how long it took to make those weird patterns to wrap around that intake-they're staying-LOL

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Good point guys. Honestly, I didn't think my wrap job would do anymore then keep the extreme heat from the header away from the bottom of the intake and keep the fuel charge a bit cooler. The wrap is only on the bottom half of each runner, and I believe there will still be plenty of heat in the intake.

I also thought I have searched and found guys that have run a heat shield all the way up against the head, so this would be different?

I would also consider the length of my intake runners-2"- maybe. Now how long are the VW runners. Just think how far the Mikuni pumps spray fuel-direct injection!! Not sure if any pooling is going to happen on this intake.

I was actually worried more about heat transfer from the intake to the carbs.

Besides-you know how long it took to make those weird patterns to wrap around that intake-they're staying-LOL

Not saying that you'll get pooling, but what you will have is a tau layer. The tau layer gets bigger as runner temp drops. This necessitates enriching the mixture.

As far as heat transfer to the carbs from the intake, do the Mikunis not have an insulator between the intake and carbs? This is pretty universal in the carb world.

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